In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) proximity service is discussed as a new function after Release 12 (see Non Patent Document 1).
The D2D proximity service (D2D ProSe) is a service enabling direct Device-to-Device communication within a synchronization cluster including a plurality of synchronized user terminals. The D2D proximity service includes a D2D discovery procedure (Discovery) in which a proximal terminal is discovered and D2D communication (Communication) that is direct Device-to-Device communication.
Here, an agreement is reached that a serving cell is capable of providing by an SIB (System Information Block) a frequency in which the D2D discovery procedure is supported and which is different from a frequency of the serving cell (hereinafter, “another D2D frequency”). A user terminal is capable of discovering another user terminal by monitoring a D2D discovery signal that is transmitted in another D2D frequency acquired by the SIB.